Simultaneous formation of FinFET and MUGFET

ABSTRACT

A method and structure comprise a field effect transistor structure that includes a first rectangular fin structure positioned on a substrate. The first rectangular fin structure has a bottom contacting the substrate, a top opposite the bottom, and sides between the top and the bottom. The structure additionally includes a second rectangular fin structure positioned on the substrate. Similarly, the second rectangular fin structure also has a bottom contacting the substrate, a top opposite the bottom, and sides between the top and the bottom. The sides of the second rectangular fin structure are parallel to the sides of the first rectangular fin structure. Further, a trench insulator is positioned on the substrate and is positioned between a side of the first rectangular fin structure and a side of the second rectangular fin structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No. 12/909,917, filed Oct. 22, 2010, issued as U.S. Pat. No. 8,524,545 on Sep. 3, 2013, the complete disclosure of which is incorporated herein by reference.

BACKGROUND

The present invention relates to integrated circuit structures, and more specifically, to a method and structure that has different transistor structures on the same substrate.

As integrated circuit structures evolve, different shapes and surfaces are utilized to increase density. Within a transistor, the semiconductor (or channel region) is positioned between a conductive “source” region and a similarly conductive “drain” region and when the semiconductor is in a conductive state, the semiconductor allows electrical current to flow between the source and drain. A “gate” is a conductive element that is electrically separated from the semiconductor by a “gate oxide” (which is an insulator) and current/voltage within the gate changes the conductivity of the channel region of the transistor.

Generally, transistor structures are formed by depositing or implanting impurities into a substrate to form at least one semiconductor channel region, bordered by shallow trench isolation regions below the top (upper) surface of the substrate. In this description, a “P-type transistor” is a positive-type transistor that uses impurities such as boron, aluminum, indium, gallium, etc., within an intrinsic semiconductor substrate (to create deficiencies of valence electrons) as a semiconductor channel region. Similarly, an “N-type transistor” is a negative-type transistor that uses impurities such as antimony, arsenic, phosphorous, etc., within an intrinsic semiconductor substrate (to create excessive valence electrons) as a semiconductor channel region.

One example of such advances is a transistor structure that has a three dimensional fin shape. The ends of the fin are usually conductive and can comprise, for example, source and drain regions of the transistor. The portion of the fin between the source and drain regions usually comprises a semiconductor, and is covered by a gate oxide and gate conductor. This structure is sometimes referred to as a FinFET (fin-type field effect transistor). The gate conductor can form multiple gates on the different planar surfaces of the three-dimensional channel region of the fin, and this structure is sometimes referred to as a MUGFET (multiple-gate field effect transistor).

SUMMARY

One exemplary embodiment herein that provides further advantages for such structures is a method of simultaneously forming different transistor structures on the same substrate. The method forms trench isolation regions in a silicon layer of a substrate to define a first silicon region and a second silicon region bounded by the trench isolation regions. The method patterns a first hardmask layer to form a first hardmask island on the first silicon region and a second hardmask island on the second silicon region and the method patterns a second hardmask layer to form a third hardmask island on the first hardmask island and a fourth hardmask island on the second hardmask island. Then, the method removes the fourth hardmask island from the second hardmask island and patterns first and second mandrels over the first silicon region and the second silicon region. Next, a third hardmask layer is formed over the substrate, and the method removes the first and second mandrels to form openings in the third hardmask layer to uncover exposed areas of the first silicon region and the second silicon region. Next, the method etches trenches into the exposed areas of the first silicon region and the second silicon region. Also, the method removes the second hardmask island.

Another exemplary method embodiment herein similarly forms trench isolation regions in a silicon layer of a substrate to define a first silicon region and a second silicon region bounded by the trench isolation regions. The method patterns a first hardmask layer to form a first hardmask island on the first silicon region and a second hardmask island on the second silicon region and the method patterns a second hardmask layer to form a third hardmask island on the first hardmask island and a fourth hardmask island on the second hardmask island. Then, the method removes the fourth hardmask island from the second hardmask island and patterns first and second mandrels over the first silicon region and the second silicon region. Next a third hardmask layer is formed over the substrate, and the method removes the first and second mandrels to form openings in the third hardmask layer to uncover exposed areas of the first silicon region and the second silicon region. Next, the method etches trenches into the exposed areas of the first silicon region and the second silicon region. Also, the method removes the second hardmask island. The method further patterns a source and drain protective layer over the first silicon region and the second silicon region. The source and drain protective layer protects source and drain regions of the first silicon region and the second silicon region and leaves channel regions of the first silicon region and the second silicon region exposed. The method then forms a gate insulator on the channel regions and patterns at least one gate conductor on the gate insulator. The method then removes the source and drain protective layer and implants an impurity into the source and drain regions.

One exemplary structure embodiment herein is a field effect transistor structure that includes a first rectangular fin structure positioned on a substrate. The first rectangular fin structure has a bottom contacting the substrate, a top opposite the bottom, and sides between the top and the bottom. The structure additionally includes a second rectangular fin structure positioned on the substrate. Similarly, the second rectangular fin structure also has a bottom contacting the substrate, a top opposite the bottom, and sides between the top and the bottom. The sides of the second rectangular fin structure are parallel to the sides of the first rectangular fin structure. Further, a trench insulator is positioned on the substrate and is positioned between a side of the first rectangular fin structure and a side of the second rectangular fin structure. Additionally, a gate conductor is positioned on the trench insulator, positioned over the sides and the top of the first rectangular fin structure, and positioned over the sides and the top of the second rectangular fin structure. The gate conductor runs perpendicular to the sides of the first rectangular fin structure and the sides of the second rectangular fin structure. Also, a gate insulator is positioned between the gate conductor and the first rectangular fin structure and between the gate conductor and the second rectangular fin structure. The structure further includes a first cap on the top of the first rectangular fin structure. The first cap separates the gate conductor from the first rectangular fin structure.

Another exemplary structure embodiment herein is a field effect transistor structure that includes a first rectangular fin structure positioned on a substrate. The first rectangular fin structure has a bottom contacting the substrate, a top opposite the bottom, and sides between the top and the bottom. The structure additionally includes a second rectangular fin structure positioned on the substrate. Similarly, the second rectangular fin structure also has a bottom contacting the substrate, a top opposite the bottom, and sides between the top and the bottom. The sides of the second rectangular fin structure are parallel to the sides of the first rectangular fin structure. Further, a trench insulator is positioned on the substrate and is positioned between a side of the first rectangular fin structure and a side of the second rectangular fin structure. Additionally, a gate conductor is positioned on the trench insulator, positioned over the sides and the top of the first rectangular fin structure, and positioned over the sides and the top of the second rectangular fin structure. The gate conductor runs perpendicular to the sides of the first rectangular fin structure and the sides of the second rectangular fin structure. Also, a gate insulator is positioned between the gate conductor and the first rectangular fin structure and between the gate conductor and the second rectangular fin structure. The structure further includes a first cap on the top of the first rectangular fin structure. The first cap separates the gate conductor from the first rectangular fin structure. In this embodiment, the gate insulator separates the gate conductor only from the sides of the first rectangular fin structure, and the gate insulator separates the gate conductor from the sides and top of the second rectangular fin structure.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a cross-sectional side view of a partially completed transistor structure;

FIG. 2 is a top view of a partially completed transistor structure;

FIG. 3 is a cross-sectional side view of a partially completed transistor structure;

FIG. 4 is a cross-sectional side view of a partially completed transistor structure;

FIG. 5 is a cross-sectional side view of a partially completed transistor structure;

FIG. 6 is a cross-sectional side view of a partially completed transistor structure;

FIG. 7 is a cross-sectional side view of a partially completed transistor structure;

FIG. 8 is a cross-sectional side view of a partially completed transistor structure;

FIG. 9 is a cross-sectional side view of a partially completed transistor structure;

FIG. 10 is a cross-sectional side view of a partially completed transistor structure;

FIG. 11 is a top view of a partially completed transistor structure;

FIG. 12 is a top view of a partially completed transistor structure;

FIG. 13 is a cross-sectional side view of a partially completed transistor structure;

FIG. 14 is a cross-sectional side view of a partially completed transistor structure;

FIG. 15 is a cross-sectional side view of a partially completed transistor structure; and

FIG. 16 is a cross-sectional side view of a partially completed transistor structure.

DETAILED DESCRIPTION

As mentioned above, FinFET and MUGFET structures are continually being developed and improved and the embodiments herein provide additional advances that allow FinFET, MUGFET, and tri-gate structures to be simultaneously formed on a substrate using damascene processing techniques (in a mandrel gate definition process). More specifically, as detailed below, the embodiments herein form a hardmask on selected ones of the fin channel structures to allow different types of transistors (single-gate, dual-gate, tri-gate, etc.) to be formed simultaneously on the same substrate. These simultaneously formed, differently gated transistors allow the performance of the circuit on the substrate to be adjusted to suite a specific design goal. The hardmask materials utilized herein can be selected to optimize etch characteristics/selectivity/and electrical isolation properties.

One exemplary method embodiment herein is illustrated in FIGS. 1-13. As shown in side-view in FIG. 1, and in top view in FIG. 2, this embodiment forms trench isolation regions 104 in a silicon layer 102, 112 of a substrate (100, 102, 112) to define a first silicon region 102 and a second silicon region 112 bounded by the trench isolation regions 104. Note that, in the drawings, the side view drawings are a cross-section along line A-A, shown in the top view drawings.

Substrate 100, 102 herein can comprise any material appropriate for the given purpose (whether now known or developed in the future) and can comprise, for example, Si, SiC, SiGe, SiGeC, Ge alloys, GaAs, InAs, TnP, other III-V or II-VI compound semiconductors, or organic semiconductor structures, etc. The substrates herein can be silicon-on-insulator (SOI) substrates that include (in addition to underlying layers) an insulator layer 100 and a silicon layer 102. The trench isolation regions 104 are well-known to those ordinarily skilled in the art and are generally formed by patterning openings/trenches 124 within the silicon portion 102 of the substrate and growing or filling the openings with a highly insulating material (this allows different active areas of the substrate to be electrically isolated from one another).

For purposes herein, an “insulator” is a relative term that means a material or structure that allows substantially less (<95%) electrical current to flow than does a “conductor.” The dielectrics (insulators) mentioned herein can, for example, be grown from either a dry oxygen ambient or steam and then patterned. Alternatively, the dielectrics herein may be formed from any of the many candidate high dielectric constant (high-k) materials, including but not limited to silicon nitride, silicon oxynitride, a gate dielectric stack of SiO2 and Si3N4, and metal oxides like tantalum oxide. The thickness of dielectrics herein may vary contingent upon the required device performance.

The conductors mentioned herein can be formed of any conductive material, such as polycrystalline silicon (polysilicon), amorphous silicon, a combination of amorphous silicon and polysilicon, and polysilicon-germanium, rendered conductive by the presence of a suitable dopant. Alternatively, the conductors herein may be one or more metals, such as tungsten, hafnium, tantalum, molybdenum, titanium, or nickel, or a metal silicide, any alloys of such metals, and may be deposited using physical vapor deposition, chemical vapor deposition, or any other technique known in the art.

The silicon portion of the substrate 102 can be doped to comprise a semiconductor. For purposes herein, a “semiconductor” is a material or structure that may include an implanted impurity that allows the material to sometimes be a conductor and sometimes be an insulator, based on electron and hole carrier concentration. As used herein, “implantation processes” can take any appropriate form (whether now known or developed in the future) and can comprise, for example, ion implantation, etc.

As shown in FIG. 3, this method patterns a first hardmask layer 106, 116 to form a first hardmask island 106 on the first silicon region 102 and a second hardmask island 116 on the second silicon region 112. The hardmask can be formed of any suitable material, whether now known or developed in the future, such as a metal or organic hardmask, that has a hardness measure greater than the substrate and insulator materials used in the remainder of the structure.

When patterning any material herein, the material to be patterned can be grown or deposited in any known manner and a patterning layer (such as an organic photoresist) can be formed over the material. The patterning layer (resist) can be exposed to some form of light radiation (e.g., patterned exposure, laser exposure, etc.) provided in a light exposure pattern, and then the resist is developed using a chemical agent. This process changes the characteristic of the portion of the resist that was exposed to the light. Then one portion of the resist can be rinsed off, leaving the other portion of the resist to protect the material to be patterned. A material removal process is then performed (e.g., plasma etching, etc.) to remove the unprotected portions of the material to be patterned. The resist is subsequently removed to leave the underlying material patterned according to the light exposure pattern.

As shown in side view in FIG. 4, the method patterns a second hardmask layer 108, 118 to form a third hardmask island 108 on the first hardmask island 106 and a fourth hardmask island 118 on the second hardmask island 116. The first hardmask layer is formed from a different material than the second hardmask layer, and has different etching characteristics than the first hardmask layer. This allows the second hardmask (the third hardmask island 108 and the fourth hardmask island 118) to be selectively removed relative to the first hardmask layer (the first hardmask island 106 and the second hardmask island 116) in an etching process that attacks the material of the second hardmask layer but does not affect the material of the first hardmask layer. Thus, as shown in FIG. 5, the method forms a protective mask 140 and, in FIG. 6, performs a selective material removal process to remove the unprotected fourth hardmask island 118 from the second hardmask island 116.

Next, as shown in FIG. 7, the method patterns first and second mandrels 110 over the first and second silicon regions 102, 112 using any of the methods discussed above. As shown in FIG. 8, the method then forms a third hardmask layer 122 over the substrate. In FIG. 9, the method removes the first and second mandrels 110 to form openings 120 in the third hardmask layer 122.

Also, in FIG. 10, the method etches the exposed areas of the first silicon region 102 and the second silicon region 112 to form trenches 124 between the trench isolation regions 104 and the first and second silicon regions 102, 112. In some of the embodiments, the trenches 124 can extend to the buried oxide layer 100. In other embodiments, discussed below, the trenches 124 extend partially into the first and second silicon and regions 102, 112.

In addition, in FIG. 10, the method performs a series of selective removal processes (selective etching) to remove the second hardmask island 106 and the third hardmask island 108, but leave the first hardmask island 106 in place. More specifically, a preliminary selective material removal process removes the second hardmask island 116. This preliminary selective material removal process does not attack the material of the third hardmask island 108, but would attack the material of the first hardmask island 106 if it were not protected by the third hardmask island 108. Therefore, the preliminary selective material removal process only removes the second hardmask island 116. A subsequent selective material removal process then removes the third hardmask island 108. In the subsequent selective material removal process, the etching agent does not attack the material of the first hardmask island 106, but does attack the material of the third hardmask island 108. Therefore, after this series of selective removal processes, only the first hardmask island 106 remains.

As would be understood by those ordinarily skilled in the art, while a series of selective removal processes are described above, the second hardmask island 116 and the third hardmask island 108 can also be removed by various masking and selective etching processes. Also, in some embodiments, the third hardmask island 108 can be left in place.

Referring now to top view FIGS. 11 and 12 and side view FIG. 13, the method then completes the transistor structures by removing the third hardmask layer 122 to leave the first silicon region 102 and the second silicon region 112 exposed (or partially exposed) as silicon fins (FIG. 11). The length of each of the fins is greater than the height of the fins, and the height of the fins is greater than the width of the fins. The method patterns a source and drain protective layer over the silicon fins (not shown). The source and drain protective layer protects source and drain regions 136, 138 of the silicon fins and leaves channel regions of the silicon fins exposed. The method forms a gate insulator 130 on the channel regions of the fins (FIG. 13). The method then patterns at least one gate conductor 132 on the gate insulator 130 (FIGS. 12 and 13). The method removes the source and drain protective layer and implants an impurity into the source and drain regions 136, 138 to make them conductive (FIG. 12). An overlying insulator is then formed, and various contacts are formed through the insulator.

As shown in FIG. 13, this process simultaneously forms both tri-gate or fin-type field effect transistor (FinFET) devices and multiple gate field effect transistor (MUGFET) devices on the same substrate. More specifically, the first silicon region (first silicon fin) 102 has a separate gate on each sidewall and such gates are electrically separated from each other by the first hardmask island or cap 106. Therefore, the first silicon fin 102 forms a MUGFET. To the contrary, the second silicon region (second silicon thin) 112 does not include any cap structure and therefore has three distinct surfaces and therefore comprises a tri-gate transistor or a FinFET. As mentioned above, in some embodiments, the trenches 124 do not extend to the buried oxide 100 and FIG. 14 illustrates the resulting structure which includes shorter sidewall regions than does the structure illustrated in FIG. 13. The different lengths of the sidewall regions can be utilized in different areas of the circuit to fine tune the characteristics of the different transistors that are formed.

Further, the first and second silicon regions can be adjacent one another and form parts of a single transistor device (FIGS. 1-14) or can be separated from one another on the substrate, and form parts of different transistor devices on the substrate (FIGS. 15-16). In addition, as illustrated in FIG. 15, if desired, different portions of the circuit can include different length sidewalls and both the first hardmask island 106 and third hardmask island 108 can be utilized as the cap.

Referring again to FIGS. 13-14, one exemplary structure embodiment herein is a field effect transistor structure that includes a first rectangular fin structure 102 positioned on the substrate. The first rectangular fin structure 102 has a bottom contacting the substrate 100, a top opposite the bottom, and sides between the top and the bottom. Also included is a second rectangular fin structure 112 positioned on the substrate. Similarly, the second rectangular fin structure 112 has a bottom contacting the substrate, a top opposite the bottom, and sides between the top and the bottom. The sides of the second rectangular fin structure 112 are parallel to the sides of the first rectangular fin structure 102.

This structure also includes a trench insulator 104 positioned on the substrate 100 and positioned between a side of the first rectangular fin structure 102 and a side of the second rectangular fin structure 112. A gate conductor 132 is positioned on the trench insulator 104, positioned over the sides and the top of the first rectangular fin structure 102, and positioned over the sides and the top of the second rectangular fin structure 112. The gate conductor 132 is a conformal rectangular structure that runs perpendicular to the sides of the first rectangular fin structure 102 and the sides of the second rectangular fin structure 112. A gate insulator 130 is positioned between the gate conductor 132 and the first rectangular fin structure 102 and between the gate conductor 132 and the second rectangular fin structure 112.

The first and second rectangular fin structures can be used as a multiple gate field effect transistor (MUGFET), or tri-gate or fin-type field effect transistor (FINFET) depending upon whether the cap 106 (and potentially 108) is positioned on the top of the first rectangular fin structure. The cap 106 separates the gate insulator 130 and the gate conductor 132 from the first rectangular fin structure 102. Alternatively, in the FINFET, there is no cap and the gate insulator 130 separates the gate conductor 132 from the sides and top of second rectangular fin structure 112.

The resulting integrated circuit chips can be distributed by the fabricator in raw wafer form (that is, as a single wafer that has multiple unpackaged chips), as a bare die, or in a packaged form. In the latter case the chip is mounted in a single chip package (such as a plastic carrier, with leads that are affixed to a motherboard or other higher level carrier) or in a multichip package (such as a ceramic carrier that has either or both surface interconnections or buried interconnections). In any case the chip is then integrated with other chips, discrete circuit elements, and/or other signal processing devices as part of either (a) an intermediate product, such as a motherboard, or (b) an end product. The end product can be any product that includes integrated circuit chips, ranging from toys and other low-end applications to advanced computer products having a display, a keyboard or other input device, and a central processor.

While only one or a limited number of transistors are illustrated in the drawings, those ordinarily skilled in the art would understand that many different types transistor could be simultaneously formed with the embodiment herein and the drawings are intended to show simultaneous formation of multiple different types of transistors; however, the drawings have been simplified to only show a limited number of transistors for clarity and to allow the reader to more easily recognize the different features illustrated. This is not intended to limit the invention because, as would be understood by those ordinarily skilled in the art, the invention is applicable to structures that include many of each type of transistor shown in the drawings.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

In addition, terms such as “right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, “upper”, “lower”, “under”, “below”, “underlying”, “over”, “overlying”, “parallel”, “perpendicular”, etc., used herein are understood to be relative locations as they are oriented and illustrated in the drawings (unless otherwise indicated). Terms such as “touching”, “on”, “in direct contact”, “abutting”, “directly adjacent to”, etc., mean that at least one element physically contacts another element (without other elements separating the described elements).

The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated. 

What is claimed is:
 1. A field effect transistor structure comprising: a substrate; a first rectangular fin structure positioned on said substrate, said first rectangular fin structure having a bottom contacting said substrate, a top opposite said bottom, and sides between said top and said bottom; a second rectangular fin structure positioned on said substrate, said second rectangular fin structure having a bottom contacting said substrate, a top opposite said bottom, and sides between said top and said bottom, said sides of said second rectangular fin structure being parallel to said sides of said first rectangular fin structure; a trench insulator positioned on said substrate and positioned between a side of said first rectangular fin structure and a side of said second rectangular fin structure; a gate conductor positioned on said trench insulator, positioned over said sides and said top of said first rectangular fin structure, and positioned over said sides and said top of said second rectangular fin structure, said gate conductor running perpendicular to said sides of said first rectangular fin structure and said sides of said second rectangular fin structure; and a gate insulator positioned between said gate conductor and said first rectangular fin structure and between said gate conductor and said second rectangular fin structure, a first cap on said top of said first rectangular fin structure, said first cap separating said gate conductor from said first rectangular fin structure, said gate insulator separating said gate conductor only from said sides of said first rectangular fin structure, and said gate insulator separating said gate conductor from said sides and said top of said second rectangular fin structure.
 2. The field effect transistor structure according to claim 1, said first rectangular fin structure comprising a multiple gate field effect transistor (MUGFET) and said second rectangular fin structure comprising a fin-type field effect transistor (FINFET).
 3. The field effect transistor structure according to claim 1, further comprising a second cap on said first cap, said second cap being positioned between said first cap and said gate insulator.
 4. The field effect transistor structure according to claim 1, said first rectangular fin structure and said second rectangular fin structure being one of: adjacent one another and forming parts of a single transistor device; and separated from one another on said substrate, and forming parts of different transistor devices on said substrate.
 5. The field effect transistor structure according to claim 1, said substrate comprising a silicon-on-insulator substrate comprising a silicon layer on a buried oxide layer, said gate conductor contacting said buried oxide layer on each side of said first rectangular fin structure and said second rectangular fin structure.
 6. A field effect transistor structure comprising: a substrate; a first rectangular fin structure positioned on said substrate, said first rectangular fin structure having a bottom contacting said substrate, a top opposite said bottom, and sides between said top and said bottom; a second rectangular fin structure positioned on said substrate, said second rectangular fin structure having a bottom contacting said substrate, a top opposite said bottom, and sides between said top and said bottom, said sides of said second rectangular fin structure being parallel to said sides of said first rectangular fin structure; a trench insulator positioned on said substrate and positioned between a side of said first rectangular fin structure and a side of said second rectangular fin structure; a gate conductor positioned on said trench insulator, positioned over said sides and said top of said first rectangular fin structure, and positioned over said sides and said top of said second rectangular fin structure, said gate conductor running perpendicular to said sides of said first rectangular fin structure and said sides of said second rectangular fin structure; and a gate insulator positioned between said gate conductor and said first rectangular fin structure and between said gate conductor and said second rectangular fin structure, a first cap on said top of said first rectangular fin structure, said first cap separating said gate conductor from said first rectangular fin structure, said gate insulator separating said gate conductor only from said sides of said first rectangular fin structure, and said gate insulator separating said gate conductor from said sides and said top of said second rectangular fin structure, and said first rectangular fin structure and said second rectangular fin structure being adjacent one another and forming parts of a single transistor device.
 7. The field effect transistor structure according to claim 6, said first rectangular fin structure comprising a multiple gate field effect transistor (MUGFET) and said second rectangular fin structure comprising a fin-type field effect transistor (FINFET).
 8. The field effect transistor structure according to claim 6, further comprising a second cap on said first cap, said second cap being positioned between said first cap and said gate insulator.
 9. The field effect transistor structure according to claim 6, said substrate comprising a silicon-on-insulator substrate comprising a silicon layer on a buried oxide layer, said gate conductor contacting said buried oxide layer on each side of said first rectangular fin structure and said second rectangular fin structure. 